Acute myeloid leukemia (AML) is a heterogeneous disorder of poor prognosis and is the most frequent form of acute leukemia diagnosed in adults. AML is a clonal malignancy characterized by the accumulation of somatically acquired genetic alterations in hematopoietic progenitor cells (Patel et al., 2012). Recurrent mutations in normal karyotype AML (which comprises nearly 50% of patients) involves a few set of around 30 genes the most recurrent being those affecting FLT3, NPM1, KIT, CEBPA and MLL (Patel et al, 2012; Welch et al, 2012). These mutations intervene in different cellular mechanisms such as self-renewal potential, cell survival/proliferation and myeloid differentiation which ultimately lead to the accumulation of undifferentiated blasts along with impaired normal hematopoiesis (Ferrara and Schiffer, 2013; Lowenberg et al., 1999; Mardis et al., 2009).
Despite chemotherapy and allogenic stem-cell transplantation regimens, AML management remains a challenge since although the bulk of leukemic cells is usually sensitive to chemotherapy, relapses occur and conduct to death. AML resurgence results from the inefficacy of chemotherapy to effectively target quiescent leukemia-initiating cells (LIC) which are able to self-renew and propagate the disease (Bonnet and Dick, 1997; Terpstra et al., 1996). Therefore, therapies aiming to restore LIC sensitivity to chemotherapy would be able to eradicate the disease.
Recently genetic studies have shown that epigenic modifications were associated with disease pathogenesis (Akalin et al., 2012; Figueroa et al., 2010) therefore providing guidance for patients treatment. Even tough, there is still a need to understand molecular mechanisms resulting from epigenetic modifications in AML (Abdel-Wahab and Levine, 2013) and this could help to better identify patients' groups for targeted therapies.
In myelodysplastic syndromes (MDS), DNA methylation has been shown to predict response to therapy (Shen et al., 2010). Furthermore, DNA methyltransferase inhibitors such as 5-azacytidine (5-AZA) or decitabine have shown to increase time to transformation of MDS in AML (Fenaux et al., 2010). However, response rates were time-limited and the molecular mechanism involved in the efficacy of DNA methyltransferase inhibitors is unknown (Garcia-Manero and Fenaux, 2011). Therefore, the identification of these molecular pathways could assist to determine new therapeutic associations able to increase the efficacy of DNA methyltransferase inhibitors.
Inventors have previously shown that iron deprivation therapy promotes monocytic differentiation of AML cells through the induction of reactive oxygen species (ROS) (Callens et al., 2010a). An analysis of gene expression patterns revealed that 30% of the most significant genes induced by iron homeostasis-targeting therapy presented a vitamin D receptor (VDR) signaling signature. Iron chelating agents acted synergistically with VD through the induction of VDR signaling and activation of downstream MAPKs pathway. Recently, inventors have shown in a retrospective study that combined iron chelators and vitamin D therapy is associated with increased overall survival in a retrospective cohort of elderly patients (Paubelle et al., 2013). Therefore, induction of VDR expression/activity is a potential therapeutic target in AML.
Inventors further investigated the correlation existing between VDR expression/activity and the molecular mechanisms involved in AML pathology and showed that VDR expression is downregulated in AML by an epigenic mechanism and that this was correlated with patient prognosis. Impaired VDR expression/activity limited tumor blast cells differentiation and increased stemness in both normal and malignant models. Combined treatment of AML cells with DNA-demethylating agents and VDR agonists blocked tumor propagation in mice, decreased cell stemness and restored LIC sensitivity to chemotherapy. Therefore, inventors propose that VDR expression controls major molecular mechanisms involved in monocyte differentiation, hematopoietic stem cell self-renewing and LIC longevity, which have consequences in AML pathogenesis.